Response-adapted Total Neoadjuvant Therapy Guided by Induction Chemotherapy in Early- and Intermediate-risk Low Rectal Cancer for Implementation of a Watch-and-wait Strategy

Inclusion Criteria: * Age: 18-80 years; no restriction on sex. * Histologically confirmed rectal adenocarcinoma with immunohistochemistry and/or genetic testing showing pMMR/MSS status. * Tumor characteristics assessed by chest-abdominal CT, rectal ultrasound, and MRI meeting all of the following criteria: 1. The lower edge of the tumor is ≤5 cm from the anal verge as measured by digital rectal examination or MRI; 2. Clinical stage cT1-3abN0-1M0 (for cT1N0, patients suitable for endoscopic resection are excluded); 3. MRF (-) (\>1 mm), EMVI (±); 4. Negative lateral lymph nodes and \<7 mm in size; 5. Maximum tumor length ≤5 cm; 6. Tumor circumference involvement ≤2/3. * After receiving at least two cycles of induction chemotherapy with the XELOX regimen, MRI assessment shows treatment response (tumor length reduced by ≥30% compared with baseline). * Completion of total neoadjuvant therapy (TNT), including long-course chemoradiotherapy and consolidation chemotherapy (radiotherapy: 25-28 fractions; chemotherapy: 6-8 cycles). * (For the prospective cohort) Provision of written informed consent for participation in this observational study. Exclusion Criteria: * Patients with a history of, or concurrent, other malignant tumors (except for cured basal cell carcinoma of the skin or carcinoma in situ of the cervix); * Patients with severely incomplete clinical data that preclude effective evaluation; * (For the prospective cohort) Patients who refuse to provide written informed consent.